1. Field of the Invention
The present invention relates to an optical pick-up apparatus for recording and/or reproducing various types of information on an optical recording medium, and more particularly, to an optical pick-up apparatus employing an optical modular device having two light sources of different power levels.
2. Description of the Related Art
Referring to FIG. 1, a conventional holographic pick-up apparatus comprises an optical module 10, integrally formed with a light source 12 for emitting a light beam and a photo-detector 17 for detecting a light beam reflected from an optical recording medium, and objective lens 16 for converging the light beam emitted from the light source 12 onto the optical recording medium 1.
The above-mentioned optical module 10 includes a substrate 2 and a housing 3. The light source 12 is installed at one side of a mount 11 that is installed on the substrate 2 within the housing 3. The photo-detector 17 is installed on the mount 11 and detects error signals and a radio frequency signal as a light beam reflected from the optical recording medium 1. In this example, an edge-emitting laser is employed as the light source 12.
Two light beams are emitted in opposite directions from the light source 12--one light beam is emitted toward the objective lens 16 and the other light beam is emitted toward a monitoring photo-detector 13, which is installed on the substrate 2. The radiant power of the light source 12 is controlled according to the incident light beam on the monitoring photo-detector 13. A hologram element 15 and a grating 14 are fitted into an opening of the housing 3. The hologram element 15 allows an incident light beam from the light source 12 to be transmitted straightforwardly, and diffracts a light beam reflected from the optical recording medium 1 toward the photo-detector 17. The grating 14 diffracts and transmits the incident light beam from the light source 12, resulting in a zeroth order light beam, .+-.1 st order light beams, and so on. Therefore, it is possible for the photo-detector 17 to detect a tracking error signal using a 3-light beam method.
The conventional optical pick-up apparatus constructed as described above has the advantage of simplifying the structure of the optical pick-up apparatus by employing one optical module and one objective lens 16. On the other hand, since the power levels of the light source 12 required for recording information on the recording medium and reproducing information from the recording medium are different, the conventional optical pick-up apparatus has the disadvantage of having to tune the power level of the light source 12 by employing an appropriate circuit.